Microsoft, in their article (KB317249): How to troubleshoot Event ID 2021 and Event ID 2022, provides a fairly robust assortment of diagnostics, for us to run when we see an "Event ID 2021" or "Event ID 2022" in our System Event Log.
The KnowledgeBase article advises us
Event 2021 is logged when there is accumulation of work items in the server service. But you must understand that the most common cause of the accumulation of work items in the server service is because the disk subsystem does not keep up with the number of requests.
Nowhere, however, does the article mention a very commonly known problem in Windows Networking, the IRPStackSize error. Yet, in one case presented in Windows XP Networking and the Web: Mapped file share unavailable within seconds, the problem mentioned was resolved in that well known way
I solved this problem by further increasing IRPStackSize, to 45 decimal ...
We should note that the KnowledgeBase article mentioned above was purposed for server operating systems, not stated to include Windows XP Home. But in this case, the client found the content of the article sufficiently interesting that he was motivated to increase IRPStackSize, and thus reached his solution.